1. Field of the Invention
The present invention relates to a bearing device for relative rotation or angular movement of a shaft and sleeve, and more particularly the invention pertains to such a bearing device for supporting a shaft and a sleeve such that the shaft and sleeve is stopped at a required relative position in a short time after being rotated or angularly displaced relatively at a substantial speed. Although not limited thereto, the bearing device of the present invention is effectively used for a pivot assembly which rotatably support an arm carrying a head for reading and/or writing data on a storage media, such as a hard disk. The present invention also relates to a storage media driving device provided with such bearing device.
2. Description of the Prior Arts
A hard disk drive generally includes a magnetic head for reading and writing data on a magnetic layer of a hard disk. The head is carried on a tip of an arm which is pivotably supported by a bearing device, conventionally referred to as pivot assembly. The bearing device is essentially composed of a stationary shaft fixed on a base or housing of the disk drive, and a sleeve coupled with the arm and supported on the shaft through a bearing such that the arm and sleeve integrally pivot on the shaft about an axis of rotation extending longitudinally through the center of the shaft, The arm is associated with a voice coil motor to be driven thereby from a rest position to a required angular position where the head opposes a required track of the disk to access and read or write data.
In recent years, the density of data to be recorded on a hard disk in a disk drive apparatuses have been increased remarkably and the processing speeds of computer have been increased. To achieve those improvements, access time of disk drive apparatuses is now required to be extremely short. To this end, it is necessary to drive, at high speed, the head to a desired position above the disk. That is, it is necessary to angularly displace the head by a required angle instantaneously. Because of the recent increase in the recorded data density on disks, width of the recording track has been made very small. Therefore, in data access operation, high preciseness is required for the positioning of the head at its read/write position. Accordingly the arm must pivot at high speed and stopped exactly at a prescribed angular position. However, as the arm is driven at higher speed, vibrations of the arm occurring after the stoppage of the arm are likely to increase infamplitude and attenuation period. To enable high-speed access in the disk drive apparatus, it is necessary to effectively attenuate the vibrations of the head assembly including the head and the arm, since data writing or reading cannot be started until the vibration disappears and the vibration attenuation time is directly added to the access time.
Conventionally, there are proposed several techniques for attenuating the vibration of the head assembly caused by stoppage of its pivotal or angular movement during the access to a desired track on the disk. For example, Japanese Unhexamined Patent Publication JP-A 62-54878 discloses a head actuator device in which a bobbin of a voice coil is provided with a damper which in turn, comprises viscous grease and a number of small-diameter damping mass bodies such as small metal balls sealed in a hermetically sealed box. Vibration is attenuated by the movement of the damping mass bodies which are enclosed by the viscous grease. Japanese Unexamined Patent Publication JP-A 64-48277 discloses another type of a damping mechanism in which a damper, comprises a weight attached to the tip of the arm via the vibration isolating rubber member. Vibration is attenuated in such a manner that the vibration isolating rubber member is deformed as the weight moves. Further, Japanese Unexamined Patent Publication JP-A 4-64979 discloses a damping device in which a hole is formed on the arm at its longitudinally middle portion and granular materials or liquid or a combination of those is sealed in the hole. Vibration is attenuated by movement of the granular materials and/or the liquid.
As described above, vibration of the head assembly is caused when its angular movement is stopped at the time of data access. To shorten the access time, it is necessary to effectively attenuate vibration of the entire head assembly. To this end, it is necessary that the damping effect is uniform around the axis of rotation of the arm, i.e. in all directions from the axis.
In the apparatus of JP-A 62-54878, JP-A 64-48277 and JP-A 4-64979, the damper is provided at the tip portion or the middle portion of the arm or on the bobbin of the voice coil. Consequently, with the conventional damping structures, damping is effected in a particular direction at a distance from the axis of rotation. Thus, the damping effect is different with the directions from the axis and is not effective and sufficient. Further, the structure in which the damper is provided at the tip portion or the middle portion of the arm or in the voice coil has a problem that vibration of the head may be amplified depending on the natural frequency of the combination of the damper and the arm (since the arm has elasticity and the combination of the damper and the arm has a natural frequency). Many hard disk drive has a plurality of heads and arms for reading and writing data on a plurality of hard disks mounted on a spindle motor. In such a case, the above mentioned conventional damping device must be provided for each of the arm, resulting increase of manufacturing process and costs.
U.S. Pat. No. 5,491,598 discloses another actuator system having a structure for attenuating vibration of the head assembly. This actuator system includes a bearing assembly for supporting an actuator arm for rotation about an axis in a disk drive. The bearing assembly includes a shaft generally defining the axis. A plurality of bearings are disposed about the shaft, and a sleeve is coupled to the bearings for rotation about the shaft. A damper is coupled to the sleeve to damp vibration of the rotary actuator in one preferred embodiment of the U.S. Pat. No. 5,491,598, the shaft has an external surface and the sleeve has an inner surface generally facing the external surface of the shaft. The damper includes a damping material coupled to the inner surface of the sleeve. The damper also includes a damping member coupled to the damping material within the sleeve.
In the damper structure disclosed by the above USP, one cylindrical damping member (i.e. a damping mass) is disposed movably around the shaft and is held by two damping materials (presumably made of viscoelastic material) in order to attach the damping member to the inner surface of the sleeve. And these two damping materials are symmetrically arranged with respect to the axis of the shaft. Such a damping structure cannot sufficiently attenuate angular vibration.
It is accordingly an object off the present invention to provide a damping device for pivoting assembly that effectively attenuate vibration of a pivoting member when it is stopped.
It is another object of the present invention to provide a well balanced damping device for effectively damping vibration of an actuator arm for a storage disk drive device.
It is yet another object of the present invention to provide a highly responsive data read/write device for a computer.
It is further object of the present invention to provide a data access mechanism in which an arm carrying data read/write head is stopped with a short vibration attenuating time even if the arm is driven at high speed.
It is still further object of the present invention to provide a data storage device in which data access time is short.
To attain the above mentioned objects, a damping mechanism according to one aspect of the present invention, comprises a plurality of, preferably more than two, damping portions circumferentially arranged around an axis of rotation of an arm which carries a head for read or write data on a disk shaped data storage media The damping portions are disposed or located at regular intervals or extensions. Each damping portion includes a holding section that movably holds or supports one or more damping mass which in turn collides or abuts against a portion of the holding section. Such collision as well as movement of the damping mass effectively attenuate the vibration caused when the arm is stopped.
The damping mechanism is coupled with a sleeve which, in turn, is supported on a shaft through a bearing mechanism and is connected with the arm to move or pivot integrally therewith in angular direction. As an alternation the damping mechanism may be coupled with other portion of the hear carrying arm driving mechanism so far as the damper is coupled with or associated with a part movable with the arm and the damping sections or elements are arranged to circularly at regular, intervals or extensions. As to the regularity of the arrangement, the damping sections or elements may preferably arranged at the same or equal intervals or extension.
According to an aspect of the present invention, one or more spherical or ball-shape damping mass or masses is accommodated in each of circularly arranged sector-shape compartments or cylindrical recesses such that the damping mass rolls in and collides against the wall of the compartment or recess to absorb the vibration energy. The spherical or ball shape of the damping mass makes the latter unstable in the compartment or recess so that the damping mechanism is responsive to even small amplitude vibration and attenuate the vibration effectively in a short time. The recess may be formed with a projection on its bottom to enhance unstableness of sustaining the damping mass, thereby making the damping mechanism more sensitive and responsive to the vibration.
In some preferred embodiments, the sector shaped compartments have the same circular extension with each other and arranged side-by-side to make a circle that is concentric with the axis of rotation of the arm. With this structure, damping is effectuated evenly around the axis of rotation. The compartments may be integrally coupled with a sleeve which is supported by a stationary shaft through a pair of ball bearings. The circle of the compartments may be disposed between the ball bearings. In an embodiment of the present invention, the circle of compartments is two in number and two circles of compartments are aligned in axial direction. Another circle of compartment may be coupled with the sleeve. A partition between each adjacent compartments may be flexible or resilient to absorb vibration energy effectively when the damping mass or masses collides against the partition. Fluid material such as liquid or granules may be in each compartment with or without the damping mass member to effectuate damping.
According to another embodiments, the damping masses may be supported, sustained or suspended by a spring or resilient rod on a holding member which may be flat plate or in a recess. In a simplified form of an embodiment of the invention, resilient or elastic rods, as collision members, are respectively associated with springs and provided on a holding plate such that they swing on the plate and the rod and spring collide each other.